For many years a lingering controversy has plagued many breast cancer patients and survivors – the question of to eat, or not to eat soy products. This question arose because soy is a source of isoflavones, compounds that are sometimes called phytoestrogens since they bind to estrogen receptor sites on cells in the body. As many breast cancers are estrogen related, the fear was that consumption of these compounds in soy products would at best prevent certain cancer therapies from working, and at worse actually be a contributing factor in the development of breast cancer.

The problem is that this idea was just a theory not based on much actual evidence. It also didn’t take into account that phytoestrogens are found in many foods that were never included in the list of things to avoid for breast cancer patients. A short sampling of other foods containing phytoestrogens includes sesame seeds, oats, barley, lentils, apples, carrots, beer, and even coffee (and the list goes on after that).

Over the last few years however, the evidence has been coming in that not only does soy consumption not contribute to cancer, but, in many patients it actually can prevent recurrence of breast cancer in breast cancer survivors. In earlier studies of Asian women, a group of people who consume much higher amounts of soy than women in the United States, soy intake was seen to actually have a protective effect against cancer (in other words, it helped prevent breast cancer, not make it more likely).

Earlier this month another large-scale study (looking at over 6000 women) was published in the journal of the American Cancer Society. This paper looked at an ethnically diverse group of women with breast cancer based in the United States, and evaluated the effect of their soy intake. According to the authors of the study, “In this large, ethnically diverse cohort of women with breast cancer living in North America, a higher dietary intake of isoflavone [soy] was associated with reduced all-cause mortality.” In other words, consumption of soy products in some groups reduced risk of dying from breast cancer. Furthermore, the study found that no group of breast cancer patients, including those with estrogen based cancers, had any negative effect from consuming soy. To read the original article please click here (the abstract is free to read although the full article requires a subscription).

At this point we can clearly say that based on scientific evidence breast cancer patients can safely consume soy products. It is important to note though that this recommendation is made about actual food, not dietary supplements. We would also recommend trying to only consume high quality soy in the form of organic soybeans, tofu, tempeh, etc… We do not recommend consuming highly processed and artificially colored or flavored soy products made for example to mimic other foods (like soy hotdogs and the like). Enjoy eating real food, and enjoy staying healthy as a result. Remember that other aspects of a healthy lifestyle, including getting adequate rest and exercise, reduce risk and recurrence of cancer as well.